The present invention relates generally to the field of tracking and/or guiding a boring tool to an underground location using an electromagnetic locating signal and, more particularly, to a system and method which provides for guiding the boring tool to any selected location within an underground region. The target location is unconstrained with respect to any system component geometric arrangements so long as the receiving position is within a receiving range of the boring tool.
One early approach taken by the prior art in tracking a boring tool employs accelerometer and magnetometer sensors in the boring tool. Information is sent to an above ground display through the use of a cable to display pitch and yaw information. In one improvement, the pitch and yaw angles of the boring tool are integrated to estimate the position of the boring tool. It should be appreciated that boring tool position relative to a target is not available in this system. Moreover, accumulation of pitch and yaw measurement errors adversely influences the estimated boring tool position.
Another, more recent, approach taken in the prior art, with regard to guiding an in-ground boring tool, embodies a xe2x80x9chomingxe2x80x9d configuration. In such a configuration, the boring tool homes-in on a receiving position at which a receiver is located. Homing configurations are generally incapable of homing-in on anything other than the receiving position itself. That is, the target of the boring tool is necessarily limited to the position of the receiver. In one improvement, U.S. Pat. No. 4,881,083 (hereinafter the ""083 patent) describes a homing configuration wherein the boring tool homes-in on a vertically oriented line extending through the receiver, in one embodiment, or homing in on the receiver itself, in another embodiment. In accordance with the former embodiment (see FIG. 1 of the ""083 patent), the receiver is positionable above a pit for purposes of drilling to some previously underground point on the vertical line below the previous surface of the ground. The system, however, does nothing with respect to monitoring the depth of the boring tool. The depth of the boring tool must be independently established or controlled for the boring tool to properly emerge in the pit. In the latter embodiment (see FIG. 8 of the (""083 patent) and consistent with the prior art in general, the system is incapable of doing any thing other than homing on the receiving position. That is, no target other than the receiving position is possible.
A marked improvement over the general state of the prior art is described as one aspect of U.S. Pat. No. 6,250,402 (hereinafter the ""402 patent) which is co-assigned with the present application and which is incorporated herein by reference. In contrast with the prior art, the ""402 patent provides for steering a boring tool to specified depth target locations that are directly below the receiver (see FIG. 9 of the ""402 patent). As described at column 27, lines 18-20 of the ""402 patent, however, even this technique is limited in that the target may not be positioned beyond or in front of the receiver. It should also be appreciated that the target may not be positioned to the side (i.e., laterally displaced) of the receiver.
The present invention serves to remove the foregoing constraints with respect to the prior art while providing still further advantages, as will be described.
As will be described in more detail hereinafter, there are disclosed herein apparatus and an associated method for tracking and/or guiding a boring tool to a selected underground location.
In one aspect of the present invention, a system is described for tracking a boring tool within an underground region. In this system, the boring tool is configured for transmitting a dipole locating signal and the position of the boring tool is characterized, at least in part, by certain orientation parameters. From a first position, the boring tool is moved to a second position during a time interval. The first position forms part of a first positional relationship relative to a receiving position. With the boring tool at the second position, a signal strength of the locating signal is measured at the receiving position as well as the certain orientation parameters of the boring tool. A maximum movement value for the boring tool is established such that any potential movement of the boring tool over the time interval is less than the maximum movement value. Based on the first positional relationship, the certain orientation parameters, the maximum movement value and the determined signal strength of the locating signal at the second position, a second positional relationship is determined including the boring tool at the second position relative to the receiving position.
In another aspect of the present invention, target coordinates are obtained to which the boring tool is to be directed. In one feature, the target coordinates are specified by a user relative to the receiving position. A target position is then determined relative to the boring tool.
In yet another aspect of the present invention, an intended path of the boring tool, extending between target and starting positions, may be longer than a dipole receiving range which defines a physical limit as to the potential distance between the boring tool and the locator, at or less than which limit the dipole locating signal is receivable by the locator. In one feature, the locator may be positioned laterally offset from the intended path. In another feature, a first position of the boring tool and a target location may be arranged to define the intended path as being approximately double the dipole receiving range.
In still another aspect of the present invention, steering commands are generated as part of a complete steering solution where desired pitch and yaw angles are specified for the boring tool at the target location in addition to the target coordinates.
In a further aspect of the present invention, a system for tracking a boring tool within an underground region is described, in which system the boring tool is configured for transmitting a dipole locating signal axially coincident with an elongation axis of the boring tool. A starting positional relationship is determined including the boring tool and a receiving position at which the dipole locating signal is to be monitored such that the receiving position is generally ahead of the boring tool. The boring tool is moved in a direction generally forward through the ground during a series of distance movements such that each distance movement is is less than a maximum movement value. For each distance movement making up a first sequence in the series of distance movements, at least measured values of the locating signal taken at the receiving position are used to determine a forward distance from the boring tool to an orthogonal plane defined normal to the elongation axis and including the receiving position. When, for a particular one of the first sequence of distance movements, the forward distance is determined to be less than the maximum movement value, the dipole locating signal is thereafter monitored during a second sequence in the series of the distance movements in a predetermined way which detects a specific one of the distance movements concluding the second sequence during which the boring tool crosses the plane.
In another aspect of the present invention, for each distance movement in a third sequence of the series of distance movements, monitoring of the dipole locating signal continues in the predetermined way for another crossing of the plane while a rearward distance is determined from the boring tool to the plane now located behind the boring tool. When the rearward distance determined following one of the distance movements concluding the third sequence is greater than the maximum movement value, for each distance movement making up a fourth sequence of the series of distance movements, at least measured values of the locating signal taken at the receiving position are used to confirm that the rearward distance is greater than the maximum movement value.
In an additional aspect of the present invention, a system is described for tracking a boring tool within an underground region, in which system the boring tool is configured for transmitting a dipole locating signal axially coincident with an elongation axis of the boring tool. A starting positional relationship is determined including the boring tool and a receiving position at which the dipole locating signal is to be monitored. The boring tool is moved through the ground during a series of distance movements such that each distance movement of the boring tool is less than a maximum movement value. For each distance movement, a current positional relationship is determined for a current one of the distance movements based on (i) a last-determined positional relationship established for an immediately preceding one of the distance movements, (ii) the certain orientation parameters, (iii) the maximum movement value and (iv) the determined signal strength of the locating signal in the current positional relationship. In one feature, target coordinates are accepted and a target position, based on the target coordinates, is included as part of the current positional relationship.
In a continuing aspect of the present invention, a system tracks a boring tool that is moved by a drill string within an underground region. Movement of the boring tool is characterized by certain orientation parameters including pitch and yaw and the system is configured at least for establishing the pitch and yaw orientation of the boring tool. Initially, a first pitch orientation and a first yaw orientation of the boring tool are determined corresponding to a first position of the boring tool. The boring tool is moved to a second position. A second pitch orientation and a second yaw orientation of the boring tool are determined for the second position as well as a distance between the first and second positions. Using the first and second pitch values, the first and second yaw values and the distance between the first and second positions, a curvature of the drill string is determined. In one feature, the first and second pitch values are used to determine a pitch angle increment and the first and second yaw values are used to determine a yaw angle increment. Thereafter, the pitch angle increment and the yaw angle increment are used, in combination, to establish an angular deflection of the drill string for use in determining the curvature of the drill string. In another feature, a ratio of the angular deflection to the distance between the first and second positions is used to determine the curvature of the drill string.
In another aspect of the present invention, a system tracks a boring tool that is configured for transmitting a dipole locating signal within an underground region where movement of the boring tool is characterized by certain orientation parameters including pitch and yaw. The system is configured at least for establishing the pitch and yaw orientations of the boring tool. Means is provided for accepting a target location to which the boring tool is to be guided including a target pitch orientation and a target roll orientation. Receiving means measures the locating signal at a receiving position. Processing means then generates steering commands for use in guiding the boring tool to the target location using (i) measured values of the locating signal taken at the receiving position by the receiving means, (ii) measurements of the pitch and yaw orientations of the boring tool, (iii) the target pitch orientation and (iv) the target yaw operation. In one feature, the processing means is configured for generating the steering commands with the target position at least laterally offset with respect to the receiving position. In another feature, the processing means generates the steering commands by producing a horizontal steering command and a vertical steering command in a mathematically coupled manner.